Steam actuated pilot controlled distribution valve for steam engines



m m, 1946. J, M 2,412,478

STEAM AC'IUATED PILOT CONTROLLED DISTRIBUTION VALVE FOR STEAM ENGINES Filed Dec. 28, 1944 Patented Dec. 10, 1946 STEAM ACTUATED PILOT CONTROLLED DISTRIBUTION VALVE FOR STEAM EN- GINES James Sim, Cathcart, Glasgow, Scotland, assignor to G. & J. Weir, Limited, Glasgow, Scotland, a corporation of Great Britain Application December 28, 1944, Serial No. 570,183 In Great Britain January 8, 1944 This invention applies to steam distributing valves of the type in which a main shuttle valve is reciprocated by steam pressure under the control of an auxiliary mechanically actuated valve sliding on the back of the main valve.

Examples of this type are represented in Figs. 1, 2, and 3 of the specification of British Letters Patent No. 3,723 of 1394 and in Figs. 1 to 9 of the specification of British Letters Patent No. 1,023 of 1881, and in a modernized form in the specification of United States Letters Patent No. 2,093,963.

With the present day increase in boiler pressures and the high superheat temperatures now being used, difficulties, particularly excessive wear, are experienced with steam slide valves of the type described in the specifications of the said British Letters Patent. These difficulties are aggravated by the modern demand that the exhaust from auxiliary engines should be oilfree. These requirements demand a steam slide valve which will operate satisfactorily with high steam pressure and superheat, without lubricating oil, and without being subject to excessive wear on the sliding surfaces.

The present invention consists of an arrangement of parts, particularly applicable to the construction described in the specification of the aforementioned British Patent No. 3,723 of 1894., and so disposed as to reduce the loading on the sliding surfaces to such a value that satisfactory operation is obtained at the highest pressures and degrees of superheat without the need for internal lubrication.

Figs. 1, 2, 3, 4 and 5 are sectional views illustrating the invention as applied to the construction according to the aforementioned British Patent No. 3,723 of 1894.

In Figs. 1 and 2 a is the valve chest casing with inlet port 8 and exhaust port 9, b and c the steam ports to the top and bottom of the steam cylinder driving the pump, d is the main steam valve or shuttle valve having steam ports I), c and an exhaust port a, e are bells or small cylinders which embrace the ends of the shuttle Valve,

and provide operating cylinders for the recipro cation of the shuttle valve. is the auxiliary valve which slides on the back face of the shuttle valve d. The valve is operated by the valve spindle g driven in usual manner from the valve gear levers of the pump. The valve 1 is a sliding fit between the collar h and nuts 1 on the valve spindle g to ensure that the valve will bed down on the back face of the shuttle valve (1.

The auxiliary valve is provided with a ma- 2 Claims. (01. 121-157) 2 a chined back'face. The valve spindle g passes through the centre of the auxiliary valve. The spindle, where it passes through the auxiliary valve, is square in section and is a fit on the sides with clearance front and back so that the auxiliary valve can bed down on the shuttle valve back face but cannot, at the same time, be moved sideways by the shuttle valve when the latter is in motion. Two holes a are drilled through the auxiliary valve to provide relief for steam leakage at the back of the auxiliary valve 1. A floating ring it is arranged on the back of and slides on the valve and bounds a space I which is brought under exhaust pressure by connection to the exhaust system of the auxiliary valve and shuttle valve through the holes it The space I is closed by the cover 112. The ring 7c is an easy sliding fit in the body of the casing 11. Grooves n are provided to allow high pressure steam to act on the top of the ring is and press the ring against the back of the auxiliary valve and thus prevent high pressure steam leaking into the space Z between the ring and the back of the auxiliary valve 1.

The intensity of pressure between the ring R: and the back of the auxiliary valve 1 may be reduced to a satisfactory amount by the construction shown in Fig. 3.

In Fig. 3 an internal fiange o is shown as formed solid with the ring is. A recess p is formed in the face of the flange o, and holes (1 are drilled through from the bottom of the recess p.' This construction increases the sliding area of the ring it in contact with the back of the auxiliary valve without causing any increase in total loading from the high pressure steam pressing on the ring is. The intensity of sliding pressure can therefore be controlled to any desired amount by the selection of suitable proportions.

Leakage of steam into the space Z at the outer end or the end remote from the auxiliary valve may be prevented by means known per se, such as shown in Figs. 3, 4 and 5.

In Fig. 3 a flexible metallic plate or disc 1 is shownjointed to the cover an. The high pressure steam admitted by the grooves 11, presses the plate 1 against the outer edge of the ring is and prevents the leakage of steam into the space 1.

In Fig. 4 a packed stuffing box or gland s is shown incorporated in the cover m to prevent the leakage of steam into the space Z.

In Fig. 5 normal type piston rings t are shown, housed in the cover m and adapted to fit within the ring lc to prevent the leakage of steam into the space I.

The sliding faces of the shuttle valve 11 and the auxiliary valve f can be entirely relieved of loading by equalising the cross-sectional areas of the exhaust cavity u of the shuttle valve, of the exhaust cavity 0 of the auxiliary valve and of the cavity Z which is under exhaust pressure because of its connection with the cavity 11. by way of the holes 7'. The loading of these faces would be entirely relieved if the ring it were solid with the body of the chest a, but this would not be a good practical construction due to the precision necessary in manufacture; but by making the ring is separate and an easy fit in the chest a there is obtained a loading of the sliding faces which depends on the thickness chosen for the ring is and is thus controllable. A certain loading is desirable and is that just necessary to hold the faces in contact.

It will be understood that the whole of the interior of the chest is under high steam pressure so that unbalance is caused solely by exhaust ports or cavities which are under exhaust pressure.

What is claimed is:

1. In a steam distribution valve of the type referred to, the combination with a valve casing having a steam port and an exhaust port, of a shuttle Valve operative in said casing and provided with steam inlet and exhaust ports and an exhaust cavity, an auxiliary valve slideable on the back face of said shuttle valve, leaving an exhaust space between the back of said shuttle valve and said casing, said auxiliary valve being provided with holes adapted to communicate with said exhaust cavity, a cover for said exhaust space, and a floating ring bounding said exhaust space laterally, one end of said ring bearing on the back face of said auxiliary valve, said ring being in engaging relation with said cover, the effective cross-sectional area bounded by said ring being approximately equal to the exhaust port area of said shuttle valve.

2. The combination claimed in claim 1 including means to prevent steam leakage into the exhaust space bounded by the ring.

JAMES SIM. 

